My vote would be:
1 Braxton Miller
2 Manti Te'o
3 Johnny Manziel
I don't disagree with your point about Tuitt and Nix--they are absolute beasts (both are back next year by the way), but Te'o is the piece that makes the machine run so well. Still, I'd rather see him win SI Sportsman of the Year than the Hiesman.
Braxton Miller has had an amazing year and if OSU beats Michigan I think he deserves it.